FIG. 7A and FIG. 7B show typical schematic structures of a group III nitride semiconductor luminescence element 20. FIG. 7A is a top view of the element, and FIG. 7B shows the cross section at A-A line of FIG. 7A. The group III nitride semiconductor luminescence element 20 is formed with a laminate (hereinafter, this may be referred as a “laminate semiconductor layer”) comprising on one surface side of a substrate 11, a n-type layer 12, an active layer 13, and a p-type layer 14; and having a mesa structure 15 at a part of the laminate semiconductor layer thereof is known. The mesa structure 15 is formed by forming the laminate semiconductor layer comprising on one surface side of the substrate 11, the n-type layer 12, the active layer 13, and the p-type layer, and then removing a part of the laminate structure by etching or so to expose a part of the n-type layer 12. A part having a plateau shape (also called as a mesa) including the active layer 13 and the p-type layer is maintained; thereby the mesa structure 15 is formed (see the patent document 1). An n-type electrode 16 is formed on the exposed surface of the n-type layer 12, and a p-type electrode 17 is formed at the surface of the p-type layer 14.
For the group III nitride semiconductor luminescence element 20 comprising the mesa structure 15, when the driving voltage is applied to the p-type electrode 17 on the p-type layer and the n-electrode 16 on the n-type layer, the current runs the pathway having a low resistance (usually the shortest pathway) between the p-type electrode and the n-type electrode, thus the current runs by concentrating at near the edge part of the mesa structure 15 (hereinafter, it will be called as a “mesa edge”) close to the n-type electrode and the p-type electrode. As a result, the current does not flow uniformly to the active layer 13, thus uneven luminescence occurs. Also, since the current concentrates at the mesa edge, a local heat generation occurs near the mesa edge. As a result, the deterioration of the luminescence element easily proceeds, and causes the decrease in the luminescence efficiency, increase in the driving voltage, and decrease in the reliability.
The patent document 2 discloses the ultraviolet semiconductor luminescence element wherein the high resistance layer having higher resistance than the p-type layer or p-electrode is formed in a shape along the shape of p-type layer side at closer side to the n-type electrode on the surface of the p-type layer. As disclosed in the patent document 2, when the high resistance layer is formed on the p-type layer close to the mesa edge, the current can be suppressed from concentrating near the mesa edge. However, due to the presence of the high resistance layer, the resistance between the p-type electrode and the semiconductor layer becomes larger, and the driving voltage becomes larger as well.
The patent document 3 discloses the semiconductor luminescence element wherein a trench is formed between the p-electrode and the n-electrode. By forming the trench, the length of the current pathway running between the p-electrode and the n-electrode is suppressed from varying, thereby the current is suppressed from concentrating to a particular part. However, in order to make the varying of the length of the current pathway sufficiently small, the depth of the trench must be deep. If the trench is made deep, the current pathway as a whole becomes longer, and the resistance becomes large, and the driving voltage also becomes large.
Further, due to various designs of the recent devices, the luminescence element having various shapes and constitution has been proposed, and also there are variety of mesa structures and designs of the electrode shapes. The art of forming the high resistance layer and the trench as mentioned in the above will increase the steps for producing the luminescence element, hence it has become difficult to correspond to the various mesa structure and electrodes shape in a timely manner.
Further particularly, the deep ultraviolet ray luminescence element having the luminescence peak wavelength of 200 to 350 nm is difficult to produce; hence the yield tends to easily decrease. Further, when the current is running, the current tends to concentrate near the mesa edge, thus such part may deteriorate due to the heat or so and the quality tends to be damaged. Thus, the development of the luminescence element capable of suppressing the deterioration caused by the current concentration near the mesa edge was in demand.